UK light heavyweight Buatsi earned a win yet disappointing debut to his career under recent management with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a close ten-round contest at the boxing arena.
But Parker had his moments, delivering effective individual punches in a fight where the approaches didn't complement each other, with constant grabbing spoiling the action.
Two judges scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest display but what defines champions? They succeed," Buatsi said in the ringside as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts felt the challenger, 31, merited the win but the British boxer suffered the second defeat of his 28-match career.
The Champion Secures Triumph in Slow Encounter
Buatsi's progress has stalled in recent years through management issues and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter willing to be aggressive in a calculated opening few rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who operated with a solid defense to narrowly win the cleaner periods.
The audience's tolerance decreased during frequent holding, with Parker going down various instances during close exchanges.
Parker ended stronger, but many rounds were challenging to assess. However, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a excellent Manchester vs Manchester fight to secure the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional memorial prior to the bout as a bell ceremony rang in honor of local hero Ricky Hatton, who died at age 46 in September.
It was the premier televised boxing event in the location since the passing of Hatton. As the concluding sound ended, the silence transitioned to a chant of "there's only one Ricky Hatton".
The competition inside the ropes reflected the sentiment. Arthur was sent to the canvas by a powerful punch flush on the chin in the second round, standing uncertainly to his feet on the referee's count.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was injured early, significant bruising appearing under his face as the duo traded punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the result with official scores of draw, narrow lead and wider gap, but the two athletes were determined and courageous, everything their hero Hatton embodied.
